SUMMARY (See instructions): Apoptosis, a form of programmed cell death, is a highly regulated mechanism involved in cellular homeostasis and organ remodeling. Although sustained inhibition of apoptosis can lead to uncontrolled cell proliferation (neoplasia), a pharmacologic approach that could prevent apoptotic cell death could have a profound beneficial impact in a variety of diseases associated with acute cellular injury. The mitochondria play a fundamental role in the two well-established molecular pathways controlling apoptosis by mediating release of cytochrome c into the cytosol This project will focus on inhibiting cytochrome c redox cycling induced oxidation of cardiolipin by the hemoprotein reductant acetaminophen. The goals of this project are to 1) investigate the mechanisms by which cytochrome c is released following cardiolipin oxidation in mitochondria and 2) establish the efficacy of acetaminophen to inhibit apoptosis in vivo at concentrations that are within the therapeutic range in humans, and 3) identify novel inhibitors of cytochrome c redox cycling as pharmacologic candidates for preventing apoptosis in vivo using an animal model of ischemia/reperfusion injury. These investigations will utilize a conjunction of methods including isolated mitochondria, cells in culture isolated from genetic variants, and various stimuli of apoptosis. The involvement of the two mitochondrial pores in these mechanisms will be tested as well as their relationship with oxidized cardiolipin. Finally, this project will assess the ability of acetaminophen to protect kidneys in vivo from ischemia/reperfusion injury induced apoptosis. Results in this proposal will provide preclinical data necessary for consideration of initial human trials in preventing apoptotic cell death associated with disorders such as myocardial infarction and stroke. Although acetaminophen is effective in inhibiting hemoprotein redox cycling induced lipid peroxidation, it is not the ideal drug for use in humans because of its associated propensity to cause hepatotoxicity, which prohibits dose escalation to enhance efficacy. In this regard, our studies will also evaluate novel synthetic compounds with the goal being to identify new potent inhibitors of cyt c redox cycling that have a high safety margin that could be further developed and eventually tested in humans.